Frequency modulation system



Nov. 29, 1949 c. R. MULLER 2,489,311

FREQUENCY MODULATION SYSTEM Filed Aug. 11, 1945 USC/UATORJ H IF "ll IF 7 A: SEE/E5 K661101708 TUBE-9 aw;

E kw 18 E 4 r" I Q ji INVEN TOR. CONRAD R. MUL LEI? ATTORM'Y ji Parasite-N v; 29.11 949 1 FREQUENCY MODULATION srs'raiu Conrad R. Muller, Montclair, N. J., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of. Delaware Application August 11, 1945, Serial No. 610,363

6 Claims. (Cl. 332-19) This invention relates to frequency modulated oscillators.

It is an object of this invention to provide a new arrangement for modulating the frequency of an oscillator.

Another object is to modulate the frequency of an oscillator through the medium of a voltage stabilizer for the oscillator. I

In accordance with the invention I provide a frequency modulated oscillator with an energizing voltage stabilizing circuit having a low impedance series regulating tub which is controlled by a high gain amplifier operating in conjunction with a constant voltage gas tube. The regulator is provided with a potentiometer circuit which is adapted to vary the bias on the control grid in the high gain amplifier which controls the output of the series regulator tube and the voltage of which is applied to the electrodes of the oscillator for the energization thereof and for the control of its frequency. In order to modulate the oscillator of this circuit I inject a modulating voltage on to the control grid of the high gain amplifier of the stabilizer so that a modulating energizing voltage is applied to the oscillator with a resultant modulation in th frequency thereof.

These and other objects and features of the invention will become more apparent upon consideration of the following detailed description of age stabilizing and frequency modulating circuit in accordance with the invention; and

Fig. 2 is a diagram in schematic form of the circuit of Fig. 1.

Referring now to the drawings, the circuit of Fig. 1 comprises an oscillator l to which an energizing voltage is supplied from a voltage stabilizing device 2 having means 3 for adjustment of its output voltage and having injected therein a modulating voltage from a modulator 4. The voltage stabilizing device is supplied with a rectifled and filtered direct current voltage over a connection 5.

In the schematic of Fig. 2, the oscillator l which comprises a push-pull Colpitts oscillator of conventional form which has applied to the plates 6 and 1 thereof an energizing voltage over a connection 8. Since this oscillator is of known form and since many other oscillators may be used instead of the one shown, further discussion of the details thereof is believed unnecessary.

' current voltage from a rectifier-filter system applied to the plat Ill thereof, and is controlled by a voltage applied to its grid II from a plate I3 of a high gain control amplifier N. The cathode |5 of the amplifier I4 is connected to ground thru a constant voltage gas tube l6 which may be a conventional neon lamp. The amplifier l4 may also include a suppressor grid' ll, ascreen grid 18 and a control grid IS. The output of the control amplifier H which is applied to the grid ll of the regulator tube may be controlled by variation of the biasing voltage on the control grid l5. This is accomplished by means of a potentiometer comprising the resistances 20, 2| connected between the line 8 and ground at 22, the resistor 2|- being variable with respect to. the control grid l9 as by adjustment 23. A modulating voltage shown as an alternating current voltage from a source 24, is applied to the control grid iii. A decoupling circuit is preferably provided in the form of a condenser 25 and a high resistor 26, the latter being disposed between the resistance 2| and the grid IS. A plate resistor 21 is provided for the plate H! in the connection to the line 8.

In the operation of this circuit, any variation in the rectified and filtered direct current voltage as obtained at the cathode l2 of the regulator tube 9 has the effect of inducing a changing of the grid bias on the control grid l9 and to cause thereby a change in the amplifier plate current which in turn is used to vary the bias on the grid l I of the regulator tube 9, the latter functioning thus as an automatically variable series resistor. A reference voltage and a fixed negative bias for the control tube is obtained by means of the constant voltage neon bulb l6 whereby voltage changes which eventually appear on the control grid of the tube are the differences of this fixed negative reference bias and of the positive voltage taken from the voltage divider 20, 2|, 23 across the output. By suitable adjustment of the means 23 the resistance between the grid [9 and ground 22 and consequently the positive voltage obtainable therefrom may be varied within suitable limits to provide a variation in the output voltage of the stabilizing device as applied to the plates 6 and I of the oscillator. Any suitable type of modulating voltage may be applied to the grid 19 as indicated to provid an amplifurther including for adjusting the output efi'ect on the direct current energizing voltage on the plates 6 and I. Condenser 25 and the resistor 26 efi'ectively serv to decouple the modulating voltage circuit from the output voltage.

control of the stabilizer circuit. The condenser efiectively decouples the direct voltage provided by the voltage, divider 2|, M n-om entering the source 24, and-the high'value of resistor 26 prevents any appreciable amount of modulation current from entering the voltage divider network. The decoupling circuit 25-26 may not be necessary if for example a pentagrid type controlled tube is used in place of the control amplifier shown in the drawing.

-- tube in series connection While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention as defined in the objects and the accompanying claims.

I claim:

1. A system for modulating the frequency of an oscillator comprising an oscillator the frequency of which is a function of electrode voltage variations, means for supplying a direct voltage for the energization of said oscillator, means for normally stabilizing said direct voltage in accordance with oscillator load variations, and means for injecting an amplitude variable signal voltage I of sufllcient amplitude into said means for stabilizing for varying the value of the direct voltage applied to said oscillator effecting a modulation in the frequency of said oscillator.

2. A system according to claim means for stabilizing the voltage includes a regulator circuit in series with the oscillator direct voltage supply controlled by-a controlling amplifier and said amplitude variable signal voltage is applied to said amplifier.

3. A system according to claiml, further including means for adjusting the output voltage of said means for stabilizing the direct voltage.

4. A system according to claim 1, wherein said means for stabilizing the voltage includes a series regulator controlled by a controlling amplifier,

wherein said source of amplitude variable voltage of said stabilizing means, and means for substantially decoupling said means for adjusting and said means for injecting a modulating voltage from each other, said means for adjusting being connected to the output oi said regulator and said amplitude variable signal voltage being applied to'said amplifier. a

5. A'system for producing frequency modulate oscillations comprising an oscillator, a regula with said oscillator i supplying direct voltage to said oscillator, a voltage stabilizing circuit for normally stabilizing the voltage output of said regulator tube in accordance with oscillator load variations including an amplifier having a control grid, an output voltage control circuit for said regulator tube having an adjustable voltage divider connection, coupled to said regulator tube output a resistor coupling said connection to saidifcontrol grid, at source of amplitude varying signals, and means coupling,

said signals source to said control grid.

6. A frequency modulating system comprising an oscillator circuit, a source of direct voltage, a nal voltages. means for applying a said direct voltage to said oscillator circuit comprising an electron discharge device having its plate resistance in series with said direct voltage supply, means for varying said plate resistance comprising said source oi amplitudevariabIe signal voltages whereby said carrier frequency is shifted in accordance with said modulating signals- I CONRAD R. MULLER.

REFERENCES crrnn The following references are of record in the file of this patent:

- TED STATES PATENT Number Name Date 1,856,665 Stoller May -3, 1932 2,064,019 Little Dec. 15, 1936 2,120,884 7 Brown June 14, 1938 2,337,214 Tunick Dec. 21, 1943 2,350,171 Laurence May 30,. 1944' 7 2,379,325 Tunick June 28, 1945' 

